A standard vertical-axis centrifuge has an upright housing with an upper wall that is normally formed with a port or manhole in turn provided with a removable cover or lid. A seal ring is compressed between the outer periphery of the cover and the upper edge of the port and a clamping arrangement is provided to hold the cover down tight on the edge of the port during use of the centrifuge with the seal compressed.
In a standard prior-art arrangement such as described in German patent 1,091,043 issued 13 Apr. 1961 to G. Panzner or Austrian patent 246,652 issued 15 Aug. 1965 to F. Zellinger et al the port is provided at one side of its upper edge with a pair of pivot lugs having holes aligned on a horizontal axis tangent to the housing and the cover is provided with a similar such pair of lugs each positioned adjacent one of the housing lugs. A common pivot shaft extends through the four lugs so that the cover can be pivoted upward away from the housing about the axis of the shaft.
The main disadvantage of this system is that the seal is stressed excessively at its region adjacent the pivot shaft. As the cover is opened and closed this part of the seal is simultaneously compressed and shifted horizontally, typically rolling it over somewhat. Such biaxial movement does not uniformly compress the seal and subjects it to friction and torsion, so that it quickly wears out adjacent the hinge region.
In order to eliminate this problem it has been suggested in German patent document 3,343,939 filed 5 Dec. 1983 by E. Aufderhaar et al to provide a system which lifts the cover straight up off the housing at least until the seal disconnects from the housing in a direction perpendicular to the plane of the seal. Such an arrangement does indeed ensure that the seal is subjected to nothing but compression. Nonetheless this system is fairly complex and requires quite a bit of room for the cover to move in.